Better support for single-node multi-service tracing

[leostera]

Hello! Thanks for the fantastic job setting up these new set of libraries :) I've been tagging along for the ride from OpenTracing, to OpenCensus, and now to OpenTelemetry and you folks have been (as we say in Argentina) "taking my fries out of the fire".

I wanted to bring a small change I've made to a forked version of opencensus-zipkin to support using it within a single Erlang node, with a single application configuration, but allowing each "service" within it to override the serviceName. This has helped me get traces that are topology agnostic (so even in a single node, the traces look like from different physical services).

The change is small and can be found here: leostera/opencensus_zipkin@8048560 -- I'd be more than happy to submit a PR if you think this is worth having in this lib.

If you think the approach is fundamentally wrong and can offer some advice on how to do this better (maybe I missed some way of configuring the apps?), I'd be happy to learn from it too!

🍻

[tsloughter]

Hey, awesome, this is something I've particularly wanted to figure out generically within OpenTelemetry.

Are your services split by OTP Application or are you wanting it to be even per-genserver?

[leostera]

I think I've normally split them by OTP application, but I can see this being useful on a per-genserver basis too, especially when starting out, since its less trouble to set up a single app that supervises a bunch of genservers than it is to figure out the application-level dependencies / start order.